Apparatus for treating objects with particles moved by magnetic force

ABSTRACT

The apparatus comprises a device for generating a rotating magnetic field, small magnetic particles capable of being moved by the rotating magnetic field, and a surface or container to confine the moving particles to a predetermined area.

United States Patent [1 1 Lovness et al.

APPARATUS FOR TREATING OBJECTS I WITH PARTICLES MOVED BY MAGNETIC FORCE Inventors: William R. Lovness, West Saint Paul; James F. Feldhaus, Oak Park Heights, both of Minn.

Minnesota Mining and Manufacturing Company, St. Paul, Minn.

Filed: Feb. 20, 1973 Appl. No.: 334,000

Assignee:

US. Cl 51/7, 51/317, 259/DIG. 46 Int. Cl B24b 31/00, B24b 1/00 Field of Search 51/7, 17, 26, 163, 313-318;

259/1, DIG. 46

References Cited UNITED STATES PATENTS Simjian 51/7 Nov. 19, 1974 2,787,854 4/1957 Simjian 5l/7X 2,880,554 4/1959 Simjian ..5l/7

FOREIGN PATENTS OR APPLICATIONS 81,618 4/1953 Norway 259/DIG. 46

Primary Examiner-Donald G. Kelly Attorney, Agent, or FirmAlexander, Sell, Steldt and Delahunt [57] ABSTRACT The apparatus comprises a device for generating arotating magnetic field, small magnetic particles capable of being moved by the rotating magnetic field, and a surface or container to confine the moving particles to a predetermined area.

5 Claims, 6 Drawing Figures PATENTEL Nov 1 9mm APPARATUS FOR TREATING OBJECTS WITH PARTICLES MOVED BY MAGNETIC FORCE BACKGROUND OF THE INVENTION This invention relates to an apparatus for treating objects with particles moved by magnetic force.

For a long time there has been a need for an apparatus which could be used to surface treat, e.g., finish or clean, irregular-surfaced solid articles. Heretofore surface finishing, e.g., polishing, descaling, deburring, and the like, has been achieved by tumbling, sandblasting, mechanical or hand buffing, or by other means which are not entirely satisfactory for various reasons. Tumbling and sandblasting are difficult to control. Sandblasting also presents a health hazard due to the considerable air-borne particulate matter produced by such an operation. Machine and hand buffing are both difficult and extremely expensive.

Prior to our invention, cleaning methods utilized cleaning baths agitated by mechanical or ultrasonic stirring devices, soaking in chemical solutions, vapor degreasing, and other less efficient or more hazardous methods. While all of these methods have some merit, each has one or more drawbacks. Solutions containing cleaning compositions are generally corrosive. Solvents used in vapor degreasing produce toxic vapors. Me-

chanical and ultrasonic agitation of cleaning solutions fail to provide the cleanliness required by some specifications.

Surface treating apparatus may be seen in Simjian U.S. Pat. No. 2,735,232, wherein an alternating magnetic field is applied to magnetizable particles to magnetize them and cause them to move in small circular or spiral paths to polish objects placed in their such paths. And, although Simjian alleges he utilizes a rotating magnetic field, his disclosure fails to teach the use of his device, as will hereinafter be shown. Rather, Simjians device generates a magnetic field which sets up a complex magnetic flux pattern causing the magnetizable particles to move as described above.'See also Hershler, U.S. Pat. No. 3,219,318, wherein motion is imparted to permanent magnets by a magnetic field which varies in direction with time, causing the mag nets to move in a complex pattern for a similar purpose. Although Hershler suggests that the magnetic field may be provided by a number of ways, he does not mention the use of a rotating magnetic field among them. These prior art devices do not utilize a rotating magnetic field and hence are far less efficient than the apparatus of the present invention.

SUMMARY OF THE PRESENT INVENTION the invention cleans (to the same degree of cleanliness) in half the time required for such prior art devices, as will be shown, providing a considerable savings in time and expense. Additionally, the apparatus of the invention can clean to a degree of cleanliness heretofore unattainable by use of prior art devices and clean a number of articles in a single cleaning operation with an unusually high degree of cleaning uniformity from article to article.

The apparatus comprises a means for generating a rotating magnetic field, magnetic particles which are capable of being rotated by the magnetic field and a surface or container for confining the magnetic particles to a predetermined area or volume. It has been discovered that magnetic particles acted upon by a rotating magnetic field will rotate on their axes and the rotating particles will revolve in an orbital path about an axis established by the center of rotation of the rotating magnetic field, Such rotation and revolution produces aggressive movement of the particles, providing unexpectedly superior surface treatment of objects placed in their path.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of one embodiment of an apparatus according to the invention, with some parts being shown in section to facilitate understanding.

FIG. 2 is a vertical section view, taken at line 22 of the apparatus shown in FIG. 1, but reduced in scale.

FIG. 3 is a graphic illustration depicting two-phase alternating current.

FIG. 4 is a plan view of a slotted annulus which may provide one component for the apparatus of the invention.

FIGS. 5 and 6 show a preferred wiring arrangement for the device depicted in FIG. 1 and its relationship to the annulus shown in FIG. 4, the annulus being shown in an expanded view revealing its entire inner edge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred device for generating a rotating magnetic field is characterized by having at least four overlapping coils or windings of insulated wire that are arranged in a generally circular pattern of opposed pairs and that are energized with two or more out-of-phase sources of alternating current, so that opposed coils are in phase but of opposite magnetic polarity.

Such a device is illustrated in FIGS. 1 and 2 wherein opposed coil pair 30a and 30b is arranged about a cylindrical container 32 and encircled by opposed coil pair 31a and 31b such that the abutting ends of the outermost coil pair 31a and 31b lie intermediate the ends of the inner coil pair 30a and 30b, producing an over lapping arrangement. Coils 30a and 3012 are energized from the same alternating current supply in such a way as to provide opposite magnetic polarity in each. Similarly, coil pair 310 and 31b are operated from the same alternating current supply so that they, too, are of opposite polarity.

The alternating currents energizing each coil pair must have a phase relationship which is not the same. FIG. 3 illustrates two alternating currents I, and I whose amplitudes are the same but whose phase relationship is If current I I were used to energize coil pair 30a, and 30b, e.g., and current I used to energize coil pair 310 and 31b, a north and south pole would be produced opposite one another in the annulus defined by the coils, which poles would rotate as the current alternates. Hence a rotating magnetic field is produced.

The speed at which the magnetic field rotates depends upon the frequency of alternating current. For a typical 60 Hz power supply, 60 revolutions will be made in 1 second, or 3,600 revolutions in 1 minute.

The presently most preferred rotating field generating device has four or more coils, which may be wound on a slotted annulus 26 such as that shown in FIG. 4. The wires forming each coil pass through slots 1-24 of annulus 26 and form overlapping coil groups A, B, C and D, as shown in FIGS. 5 and 6.

The annulus upon which the wires are wound may be formed of laminae of high permeability steel containing from 0.25 percent to about 3.50 percent silicon, individual laminae being generally from 0.005 to 0.100 inch thick. The laminae may be coated with an insulating varnish to reduce eddy-current losses.

A simple embodiment of the rotating field generating device described above may be provided by the stator ofa conventional AC electric motor, with some modification thereof. Alternatively, the rotating field generating device can be disposed within a cylindrical container and used to rotate magnetic particles about its exterior surface. Such a generating device would resemble the rotating part of two pole wound rotor-type electric motor. Additionally, a rotating field generating device for moving the magnetic particles on a flat surface may be prepared by formingcoil slots circumferentially about one end of a suitable cylinder, inserting the coils and energizingthe coils, thus producing arotating field adjacent the end. Magnetic particles on a flat or otherwise shaped surface adjacent the end will be revolved about the axis of rotation of such a device. It is also possible to generate a rotating magnetic field by mechanically revolving permanent magnets either around or within the container.

As previously mentioned, the apparatus utilizes magnetic particles, each of which is an individual permanent magnet and hence susceptible to the influence of an electro-magnetic field. Such particles include gamma iron oxide (Fe o hard barium ferrite, (BaO 6Fe O particulate aluminum-nickel-cobalt alloys, or mixtures thereof. Suitable magnetic particles have been found to have a magnetization (M) in excess of 10 gauss per gram, magnetization being a measure of the magnetic field intensity of the material from which the particles are prepared. Hard BaO 6Fe O has a magnetization of about 70 gauss/gm. and gamma Fe O has a magnetization of about 50 gauss/gm. Also, it has been found that suitable magnetic particles should have a magnetic coercivity (defined as the opposite sign field necessary to reduce the magnetization to zero) greater than the electro-magnetic field (H) applied to cause physical movement of the particle. Electro-magnetic fields of about 100 to about 1000 oersteds and higher have been used to move the particles. Hard BaO 6Fe 0;, has a magnetic coercivity of about 3000 oersteds and gamma Fe O has a magnetic coercivity of about 300 oersteds. Magnetic particles having a magnetic coercivity less than about 100 oersteds have been found not to be particularly suited for use in the invention be-- cause application of external electro-magnetic fields sufficiently strong to move the particles causes demagnetization. Application of an electro-magnetic field to the permanently magnetic particles causes them to experience a torque tending to rotate them to an alignment parallel to the field. Rotation of the magnetic field causes the particles to rotate on their axes and to revolve in an orbital path about the axis defined by the rotating field.

The size of the magnetic particles will vary over a considerable range depending upon the particular use. For cleaning, the particles may be between 0.01 -20 microns in diameter, or larger. Other applications, e.g., grinding, polishing, burnishing, ball-milling, etc., may utilize particles from 0.1 micron to 2 inches in diameter, or larger.

For some applications it may be advantageous to pro vide the magnetic particles with an inert coating to protect them from chemical attack by the media in which they are used. For other applications it may be advantageous to provide the magnetic particles with an abrasive coating to increase their abrasiveness.

The magnetic particles may be used in a gaseous atmosphere such as air or in a carrier liquid such as water, kerosene, carbon tetrachloride, acetone, benzene, toluene, perchloroethylene, etc. The carrier liquid should be chosen so that it will not react with the magnetic particles or the articles being cleaned or polished. The carrier liquid may contain additional components such as abrasive particles, bactericides, pH regulators, alkaline builders, buffing agents, softeners, surfactants,

etc. I

For cleaning operations, the incorporation of a cleaner in the carrier liquid is required. The specific cleaner composition preferably utilized is one which would normally be used to clean the articles and which is compatible with the carrier liquid. Oil-based cleaners are generally used with organic solvent carrier liquids, and surfactants are generally used with aqueous carrier liquids. The pH of the carrier solution should not be excessively high or low because strongly acidic or strongly alkaline solutions may attack the particles or the articles being cleaned.

If desired, non-magnetic particles such as abrasive particles or particles which may be non-abrasive or weakly abrasive (e.g., small glass spheres) may be incorporated into the liquid cleaner to obtain enhanced cleaning. Additionally, surfactant may be coated on the magnetic particles to provide enchanced cleaning; surfactant coated magnetic particles are disclosed in Feldhaus US. Pat. No. 3,695,934. For effective cleaning, the volume ratio of particulate (whether magnetic particles or abrasive particles) to liquid is in the-range of about 1:100 to 302100, preferably'about 152100 to 25:100.

Cleaning or polishing of' objects is preferably achieved by placing the object to be cleaned, magnetic particles, carrier liquid (if used), abrasive particles (if used), and cleaner (if used) in a non-magnetic container within the rotating field generating device. The rotating field is generated by energizing the previously described coil arrangement with alternating current.

In accordance with the invention, apparatus comprised of a rotating field generating device, container, and magnetic particles was used to clean synthetically soiled test tags to determine cleaning efficacy. Additionally, prior art devices according to aforementioned US. Pat. Nos. 2,735,232 and 3,219,318 were prepared and also evaluated for cleaning efficacy for purposes of comparison. When the evaluations were made, care was taken to operate each device in a particular test situation at the same energy level per unit volume of magnetic particles.

The magnetic particles used in the evaluations described below consisted of surfactant-coated barium ferrite particles prepared by mixing 2000 parts distilled water, 400 parts of an aqueous solution of 30 parts polyethylene glycol ether surfactant (Tergitol v-S- l2), 15 parts polyethylene glycol ether surfactant (Tergitol l5-S-5), 5 parts triethanol amine and 50 parts water, 800 parts one-micron unmagnetized barium ferrite, and 800 parts SOO-mesh silicone carbide abrasive powder, then ballmilling the mixture for 16 hours, and finally magnetizing the mixture by briefly exposing 400 gram portions thereof to a 6000-10000 gauss magnetic field. (In the mixture described above, and in the description which follows all parts are by weight unless otherwise specified.)

The effectiveness of cleaning utilizing both the apparatus of the invention and the prior art devices was determined by first soiling round aluminum tags with a predetermined amount of synthetic soil, cleaning the articles, and determining the amount of residual soil. The aluminum tags, 24 gauge and 1% inch diameter, were first polished to a surface roughness of RMS-l2 micro inches, thoroughly cleaned, and then synthetic soil applied.

The synthetic soil-was comprised of 1.2 parts by weight anhydrous lanolin, 0.0485 part C tagged 1- micron carbon black, 29.3 parts untagged carbon black, 23.4 parts magnesium silicate, 117 parts kerosene, and 29.3 parts lubricating oil. This mixture was first ball milled 1 hour, then painted in the center of one surface of the tag as a three-fourths inch diameter dot and dried thereon at 65C. for 1 hour.

The initial concentration of radioactivity is determined with a gas Geiger counter and the tags are then subjected to various surface treatment procedures as hereinafter described, the radioactivity again determined. The amount of residual radioactivity was subtracted from the initial concentration, the difference divided by the initial radioactivity and the product multiplied by 100, the result being expressed as percent soil remaining" in tabular form below.

EVALUATION NO. 1

The apparatus according to the invention included a rotating magnetic field generating device which was originally a one-half horsepower electric motor stator comprised of a ring-like lamination (formed of 53 0.029-inch thick high permeability steel annuli) having a 5.5-inch outer diameter, a 2.8-inch inner diameter and having 24 slots uniformly about its inner circumference, with windings formed of insulated copper wire of the size designated below, forming a two pole single phase arrangement. The lamination is shown in FIG. 4 by reference numeral 26 with the slots being numbered from 1 to 24. FIG. 5 shows the placement of the starting windings with respect to the slots of the laminations, the windings forming coil groups A and B, and FIG. 6 shows the placement of the running windings which form coil groups C and D. The A coil group was wound with the same number of turns as the B coil group, and the C coil group with the same number of turns as the D coil group in the following manner:

Starting Winding (21 AWG copper) SIQ!L -Continucd Starting Winding (21 AWG copper) Slots Group A Group 8 Turns Sand 8 l7 and 20 [4 Running Winding (19 AWG copper) Slots Group A Group B Turns 7and l8 6and l) 56 8 and 17 5 and 20 52 9 and I6 4 and 19 46 lOand l5 3and 18' 37 llandl4 2andl7 18 The stator was modified to provide a phase difference as close to 90 as possible by adding a 215-259 microfarad capacitor in parallel with its existing 324-389 microfarad starting capacitor and energized with 24 to 36 volts at 60 Hz, producing an energy input of 88 watts per cubic inch.

A 400 ml Pyrex glass breaker was situated within the opening of the device described above to contain magnetic particles and five of the test tags were held on a rack within the beaker.

The prior art device, made according to FIG. 1 of US. Pat. No. 3,423,880, consisted of a 3-inch diameter, 4-inch long cylindrical tank having a solenoid formed of 400 turns of 18 AWG insulated copper wire on a steel laminate adjacent one side of its cylindrical wall. Five of the previously described soiled test tags were attached on a rack within the tank. The tank then was filled with the previously described magnetic particles and the apparatus was operated with 60 Hz current at a voltage sufficient to provide 8.8 watts per cubic Table l Soil Rem'linina Run Time US. Pat. No. Present (sec) 3,423,880 S.D.' lnvention SD.

21 6 6 3 I6 7 2 l I50 6 5 Standard deviation The prior art device moved the magnetic particles in a linear path away from the surface adjacent the solenoid, producing a stream which separated at the opposite surface and attempted to converge again at its source, the gross effect being movement of the particles in small circular paths. The apparatus of the invention, on the other hand, moved the particles in a circular path about a single axis defined by the axis of the rotating field generating device.

As is apparent, the apparatus of the present invention cleaned the test tags much faster than did the prior art device. For an equivalent run time, i.e., 120 seconds,

the apparatus of the invention had cleaned 800 percent better than the prior art device. 1

EVALUATION NO. 2

Table 2 Soil Remainin Run Time U.S. Pat. No. Present (seC.) 3,423,880 SD. Invention SD.

Standard deviation cl EVALUATION 3 The apparatus according to the invention included a rotating magnetic field generating device comprised of a 3%-inch high, lO- /-inch outer diameter, 6-%-inch inner diameter annulus having 27 slots equally spaced about its inner wall, the device being wired in a 3 phase arrangement with 136 turns of number insulated copper wire per coil. The magnetic particle container, 5inches in diameter and 3%-inches long, was fitted within the central opening of the annulus. Test tags were held in the container on a rack therefor, and the container was filled with magnetic particles.

The prior art device was a 3 pole annular arrangement prepared according to FIG. 3 of US. Pat. No. 2,735,232 approximately the same size as the apparatus described in the previous paragraph, including the same size particle container. Each of the poles was wound with 200 turns of 18 AWG insulated copper wire.

Test tags were attached to racks in the containers of each device and their containers filled with the magnetic particles described above. Both devices were energized at 6.3 watts per cubic inch'for 30 second time periods as described above with results as follows:

Standard deviation EVALUATION NO. 4

The apparatus according to the invention included a I into the bore of the stator to contain the magnetic particles and test tags.

The prior art device was a 4 pole annular arrangement prepared according to FIG. 4 of US. Pat. No. 2,735,232 approximately the same size as the apparatus described in the previous paragraph. Each pole was wound with 180 turns of 15 AWG insulated copper wire and connected as shown in the aforementioned patent drawing.

Utilizing equivalent amounts of magnetic particles and test tags, the devices were operated at 6.3 watts per cubic inch for 30 second periods with results as follows:

Table 4 Soil Remaining FIG. 4 Run Time US. Pat. No. .Present (sec) 2,787,854 S.D. Invention SD.

30 50 l7 l0 8 60 23 ll 2 3 7 5 Standard deviation What is claimed is: 1. An apparatus for treating objects with particles moved by magnetic force comprising in combination:

a. means for generating a rotating magnetic field,

b. magnetic particles which are capable of being rotated by the magnetic field, and

0. means confining the rotating magnetic particles to a predetermined area within the effective influence of said magnetic field, wherein said means for generating a rotating magnetic field comprises at least four overlapping coils that are arranged in a generally circular pattern of opposed pairs and that are energized with two or more out of phase sources of alternating current so that opposed coils are of opposite magnetic polarity and of the same phase, and generation of said rotating magnetic field causes rotation of the magnetic particles on their axes and also causes their rotation in an orbital path about the axis of rotation of the rotating field and objects placed in their path are subjected to aggressive surface treatment.

2. The apparatus of claim I wherein the magnetic particles have a magnetization of about 50 gauss/gm. and a magnetic coercivity of at least oersteds.

3. Method for treating objects with particles moved by magnetic force comprising:

' confining magnetic particles to a predetermined area,

generating a rotating magnetic field with a single axis of rotation within said predetermined area, said magnetic field comprising at least four overlapping coils that are arranged in a generally circular pattern of opposed pairs that are energized with two or more out of phase sources of alternating current so that opposed coils are of opposite magnetic polarity and of the same phase, said magnetic field being of sufficient intensity to cause rotation of the magnetic particles on their axes and also to cause their rotation in an orbital path about the axis of rotation of the rotating field, and

placing the object to be treated within the path of moved by magnetic force comprising in combination:

a. means for generating a rotating magnetic field,

b. magnetic particles which are capable of being rotated by the magnetic field, and

c, means confining the rotating magnetic particles to a predetermined area within the effective influence of said magnetic field, wherein said means for generating a rotating magnetic field comprises overlapping coils that are arranged about said predetermined area and that are energized with two or more out of phase sources of alternating current which will produce a rotating magnetic field having a single axis of rotation within said predetermined area, and generation of a rotating magnetic field causes rotation of the magnetic particles on their axes and also causes their rotation in an' orbital path about the axis of rotation of the rotating field and objects placed in their path are subjected to aggressive surface treatment.

5. Method for treating objects with particles moved by magnetic force comprising:

confining magnetic particles to a predetermined area, I

generating a rotating magnetic field with a single axis of rotation within said predetermined area by use of a generating device therefor comprising overlapping coils that are arranged about said predetermined area and that are energized with two or more out of phase sources of alternating current, said magnetic field being of sufficient intensity to cause rotation of the magnetic particles on their axes and also to cause their rotation in an orbital path about the axis of rotation of the rotating field,

and

placing the object to be treated within the path of said rotating magnetic particles for a period of time sufficient to cause surface treatment thereof. 

1. An apparatus for treating objects with particles moved by magnetic force comprising in combination: a. means for generating a rotating magnetic field, b. magnetic particles which are capable of being rotated by the magnetic field, and c. means confining the rotating magnetic particles to a predetermined area within the effective influence of said magnetic field, wherein said means for generating a rotating magnetic field comprises at least four overlapping coils that are arranged in a generally circular pattern of opposed pairs and that are energized with two or more out of phase sources of alternating current so that opposed coils are of opposite magnetic polarity and of the same phase, and generation of said rotating magnetic field causes rotation of the magnetic particles on their axes and also causes their rotation in an orbital path about the axis of rotation of the rotating field and objects placed in their path are subjected to aggressive surface treatment.
 2. The apparatus of claim 1 wherein the magnetic particles have a magnetization of about 50 gauss/gm. and a magnetic coercivity of at least 100 oersteds.
 3. Method for treating objects with particles moved by magnetic force comprising: confining magnetic particles to a predetermined area, generating a rotating magnetic field with a single axis of rotation within said predetermined area, said magnetic field comprising at least four overlapping coils that are arranged in a generally circular pattern of opposed pairs that are energized with two or more out of phase sources of alternating current so that opposed coils are of opposite magnetic polarity and of the same phase, said magnetic field being of sufficient intensity to cause rotation of the magnetic particles on their axes and also to cause their rotation in an orbital path about the axis of rotation of the rotating field, and placing the object to be treated within the path of said rotating magnetic particles for a period of time sufficient to cause surface treatment thereof.
 4. An apparatus for treating objects with particles moved by magnetic force comprising in combination: a. means for generating a rotating magnetic field, b. magnetic particles which are capable of being rotated by the magnetic field, and c. means confining the rotating magnetic particles to a predetermined area within the effective influence of said magnetic field, wherein said means for generating a rotating magnetic field comprises overlapping coils that are arranged about said predetErmined area and that are energized with two or more out of phase sources of alternating current which will produce a rotating magnetic field having a single axis of rotation within said predetermined area, and generation of a rotating magnetic field causes rotation of the magnetic particles on their axes and also causes their rotation in an orbital path about the axis of rotation of the rotating field and objects placed in their path are subjected to aggressive surface treatment.
 5. Method for treating objects with particles moved by magnetic force comprising: confining magnetic particles to a predetermined area, generating a rotating magnetic field with a single axis of rotation within said predetermined area by use of a generating device therefor comprising overlapping coils that are arranged about said predetermined area and that are energized with two or more out of phase sources of alternating current, said magnetic field being of sufficient intensity to cause rotation of the magnetic particles on their axes and also to cause their rotation in an orbital path about the axis of rotation of the rotating field, and placing the object to be treated within the path of said rotating magnetic particles for a period of time sufficient to cause surface treatment thereof. 